The long-term objectives of this Project are to define the microbial complexes that are most compatible with periodontal health leading to therapeutic and/or preventive strategies to produce the desired plaque composition Specific Aim 1 will examine periodontally health subjects in order to determine the composition of their subgingival plaque and the associations among species within the plaque samples. The data will be used to seek differences in bacterial profiles among health subjects and examine differences between periodontally healthy subjects and subjects who have periodontitis and who are on periodontal maintenance. In this cross- sectional study, 100 periodontally healthy subjects will be assessed clinically at 6 periodontal sites per tooth. Subgingival plaque samples will be take separately from the mesial aspect of each tooth and evaluated individually for their content on 40 bacterial species using checkerboard DNA-DNA hybridization. The dissemination of species from host to host is important for their intraoral survival. Specific Aim 2 will determine if family members of index subjects colonized by low levels and prevalence than family members of high-red-complex colonized index subjects. 30 high and 30 low red complex index subjects will be chosen and their spouses, siblings, parents or children examined clinically and for subgingival plaque composition (as described for SA1). Data will be used to determine if colonization by low or high levels of red complex species is a trait within families. Specific Aim 3 will determine if strains of B. forsythus, P. gingivalis and T. denticola in families show identical DNA base sequences for selected genes, suggesting transmission within the family. The method will involve PCR amplification of the chosen gene directly from plaque samples, followed by sequencing of the product. The proposed studies will clarify the composition of subgingival plaque in periodontally healthy subjects, determine if one or more healthy profiles exist, compare healthy profiles to profiles of diseases subjects before and after therapy, provide a data base for examining important bacterial associations in plaque, determine if colonization by high or low levels of the presumed pathogenic red complex is a trait exhibited within families and determine how frequently transmission occurs within families.